1. Field of the Invention
The present invention relates to a method for molding a resin-molded article having a skin integrally molded on-a part of the surface thereof, such as an instrument panel for an automobile.
2. Description of the Related Art
While a resin-molded article made from a synthetic resin is employed as an instrument panel or a door trim for an automobile, it partially has a skin on its surface to improve the physical properties and the surface appearance.
As shown in FIG. 12, for example, a resin-molded article 9 partially having a skin on its surface consists of a resin-made part 91 which is a synthetic resin body having a skin 95 integrally molded thereto.
The skin 95 can have, for example, a vinyl chloride layer on the front surface and a polypropylene foam layer on the back surface.
The conventional resin-molded article is molded by placing a skin on a portion of the inner wall of a cavity of a mold and then injecting a synthetic resin into the cavity from a gate 8 (FIG. 12) toward the skin 95.
However, the resin-molded article 9 molded as described above may undergo intrusion of the synthetic resin 91 far onto the front surface at the edge of the skin 95 as shown in FIG. 12, thereby forming a resin-intrusion 910. As a result, the appearance of the resin-molded article 9 is adversely affected.
Therefore, the object of the present invention is to provide a method for molding a resin-molded article having an excellent surface appearance without formation of any resin-intrusion on the front surface of the skin.
In the first aspect of the present invention, the present invention provides a method for molding a resin-molded article by placing a skin on a portion of an inner wall of a mold and then injecting a synthetic resin into a cavity of the mold to effect an integral molding of a resin-molded article with the skin on a portion thereof.
The mold has a first gate on a first inner wall part located away from the back surface of the skin which has been placed on the inner wall of the molding. A second gate is located on a second inner wall and facing the back surface of the skin.
The synthetic resin is first injected from the first gate until a resin comes close to the edge of the skin, and then the synthetic resin is injected from the second gate.
A key feature of the first aspect of the invention is that the injection of the synthetic resin is performed by injecting the synthetic resin initially from the first gate until the tip portion of the synthetic resin comes close to the edge of the skin and then subsequently injecting the synthetic resin from the second gate.
The effects and the advantages of the first aspect of the present invention are discussed below.
A skin is placed on a portion of the inner wall of a mold as described above, and after mold clamping, a synthetic resin is injected from the first gate. Then the synthetic resin is continuously injected until its tip portion comes close to the edge of the skin.
Subsequently, before the tip portion of the synthetic resin from the first gate comes to the edge of the skin, the synthetic resin is injected from the second gate. Injection, this time, is performed toward a back surface of the skin. Then, the synthetic resin moves through the space between the back surface of the skin and the second inner wall of the mold toward the edge of the skin, where a top of flow of the resin from the second gate fuses with the tip portion of the synthetic resin injected from the first gate at a point near the edge of the skin.
It is important here that the synthetic resin injected from the second gate presses the skin in the direction of the inner wall of the mold since it is injected onto the back surface of the skin. As a result, the edge of the skin is also pressed in the direction of the inside of the inner wall, whereby preventing the intrusion of the synthetic resin onto the front surface of the skin.
Moreover, since the tip portion of the synthetic resin injected from the first gate goes only to the point just before the edge of the skin, the intrusion described above is also prevented. As a result, a final resin-molded article has a satisfactory surface appearance on the front surface of the skin.
In the second aspect of the present invention, the present invention provides a method for molding a resin-molded article comprising placing a skin on a part of the inner wall of a mold and then injecting a synthetic resin into a cavity of the mold to effect an integral molding of a resin-molded article having the skin on a part thereof.
The method uses a mold which has a second gate on the second inner wall part which faces the back surface of the skin which has been placed on the inner wall of the mold and a first gate on a first inner wall part located away from the back surface of the skin. The method comprises the steps of:
injecting the synthetic resin only from the second gate; and
performing dwelling by pressurization from the first gate which is subsequently opened after the completion of injection of the synthetic resin from the second gate.
A key feature in the second aspect of the invention is that a mold employed only has a second gate from which a synthetic resin is injected. After completion of the injection from the second gate, a first gate is opened to effect dwelling by pressurization from the first gate.
The mold described above has a first gate and a second gate. The first gate is closed during injection of a synthetic resin.
The effect of the second aspect of the invention is discussed below.
In the second aspect of the invention, a skin is placed on a part of the inner wall of a mold as described above, and after mold clamping, a synthetic resin is injected only from the second gate. The injected synthetic resin from the second gate fills the entire cavity of the molding. As a result, the synthetic resin injected from the second gate is initially brought into contact with the back surface of the skin, and then spreads in the mold and presses against and spreads to the edges of the skin. Subsequently, the resin goes beyond the edge of the skin toward the portion of the wall which is not covered with skin.
Accordingly, no synthetic resin goes around the edge of the skin to the front surface of the skin, thereby ensuring the prevention of a peeled skin which causes a quality problem.
The injection of the synthetic resin is performed only from the second gate. Therefore, there is no need for fusion of the resin from the second gate with the synthetic resin injected from another gate, thereby ensuring the prevention of a weld which tends to form at the point of fusion.
The mold described above is provided with a first gate on the first inner wall located away from the back surface of the skin, and after completion of the injection of the synthetic resin from the second gate, the first gate is opened to effect dwelling by pressurization from the first gate.
Thus, the dwelling by which the synthetic resin is kept under pressure is performed for a period after the synthetic resin has filled the cavity. In this step, such dwelling is performed preferably utilizing the first gate described above and the pressurization by the second gate is discontinued. By such a procedure, a direct and excessive pressurization from the second gate onto the skin can be avoided, thereby reducing damage to the skin substantially. As a result, the conventional problems experienced frequently, such as a depressed skin, can be avoided.
According to the first and second aspects of the present invention, a method for molding a resin-molded article having an excellent surface appearance without forming a resin-intrusion on the front surface of the skin is provided.